Characterization and Analysis of Copper Heap Leaching by X-ray Computed Tomographic Techniques

J D Miller1, C L Lin1, C Roldan1 and C Garcia2

1 Department of Metallurgical Engineering, University of Utah, 135 South 1460 East, Room 412, Salt Lake City, Utah 84112, USA, cllin@mines.utah.edu

2 Compañía Minera Zaldívar, Av. Grecia 750, Antofagasta, Chile

ABSTRACT

Detailed analysis of copper heap leaching systems should involve both the chemistry/biochemistry and mechanics of the system. Optimum design of the chemistry, utilization of reactants (acid, air, microorganisms, bacteria population, iron), is limited by our current understanding of the mechanics of the system. Mechanics of the copper heap leaching system include such issues as particle breakage/exposure/liberation, particle texture/composition, and fluid flow phenomena inside the packed bed of particles which constitute the heap. Once these issues (such as how particle size distribution influences both mineral exposure/liberation and flow behavior) are resolved more appropriate heap designs and an optimal chemical schedule can be established.

The ultimate recovery in a heap leaching operation is related to the degree of exposure of the valuable minerals in comminuted particles. Until recently it has not been possible to accomplish mineral exposure analysis by traditional mineralogical techniques due to stereological limitations. It is important to note that exposed copper mineral grains can be identified only through 3D analysis of multiphase particles. Recently, high-resolution cone beam x-ray microtomography (XMT) has been used to provide true 3D exposure analysis of packed particle beds and is able to quantitatively describe the 3D distribution of micron-sized mineral grains in multiphase particles. XMT technology consists of examining the extent of mineral exposure for each size fraction of ore in 3D, then, by algebraic calculations, the ultimate recovery can be estimated for different particle size distributions (PSD). To confirm the usefulness of such mineral exposure analysis, column leaching tests were performed using three particle size distributions from each of three composites obtained from the copper heap leaching operation at Zaldivar-Chile.

Keywords Heap leaching, 3D exposure analysis, X-ray microtomography, particle size distribution